Cue will make the sane observation with pike spanners if they are kept in ponds that 

 are too small. 



The i^avfpr of inbreeding of stock with resulting deterioration and latent disease 

 appearance by crossing is not all too greatly to be feared. Fish and their parents with 

 visible hereditary' defects (especially malformations of all kinds) are to be removed. 



As long as no ill effects are noticeable (or no new characteristics are intended), 

 the introduction of strange carp, of unknown hereditary characteristics among well c\xlti- 

 vated stock is always risky and ought to be avoided. 



If on the other hand, it becomes noticeable that frequent introduction of fresh 

 blood increases the resistance against diseases, such a course is obviously to be recom- 

 mended, eventually even if other qualities should suffer. 



Lack of resistance against certain plagues is one of the gravest dangers of modem 

 pond culture . 



In order to aid the small fishbreeder in the selection of reliable fresh blood, the 

 respective agid cultural departments now issue diplomas to hatcheries which conduct their 

 establishments upon the most rational basis, and have necessary breeding arrangements, 

 and health requirements. 



Such hatcheries keep their stock continuously under the COTitrol and supervision of 

 scientifically trained experts and the small fishbreeder is thus assured of good material 

 for the freshing-up of his own stock. 



B. Carp Culture upon a large scale . 



I. Size and division of the necessary pond area . 



Since the rearing of carp requires a relatively large area, it is evident that 

 carp fisheries can be profitably conducted only then, when the necessary terrain is 

 available. The minimal requirement for such fisheries is an area from between 30 to 50 

 hectars (about 90 to 150 acres). 



m II I I n ti u in>« 



Fig. 15. Pondfishen" Reckahn . Ground Plan of a North German Carp and 

 Tench Pond Industry. Total area 75 hectars. Example of a standardly arranged 

 larger stock-growing fishery: Spawning and brood ponds are situated at the 

 water inflow, good reservoir constructions (compare also Fig. 59), separate 

 coverage and drainage facilities of individual ponds. 



78 



